The antenna is an essential component in wireless communication. As the demand for the amount of wirelessly transmitted data increases, the availability of a large bandwidth, such as a 7 GHz bandwidth for the 60 GHz band millimeter-wave, allows for a wide variety of applications in communication. On the other hand, due to the advancement in semiconductor manufacturing technology, the millimeter-wave single chip radio-frequency integrated circuit (RFIC) can be fabricated by many commercial foundry services. In comparison to the conventional module fabricated by discrete components, the integrated chip can reduce the module size, decrease the complexity in assembly, lower the manufacturing cost, and provide the essential function of beam switching.
Using the millimeter-wave as an example, since the 60 GHz millimeter-wave loses a large amount of transmission in the atmosphere, it requires more EIPR (Equivalent Isotropically Radiated Power) to compensate for the transmission loss and achieve the requirement of high-speed data transmission. EIPR is the product of the output power of transmitter (PTx) and the antenna gain (Gain), that is, EIRP=PTx×Gain. However, the power-add efficiency (PAE) for the current design of silicon-based solid-state amplifier operated in the millimeter-wave band is roughly around 10%, and the output power is also very limited. Therefore, increasing the antenna gain becomes the most effective method in order to improve the EIRP.
The size of the antenna is proportional to the wavelength. The wavelength of the millimeter-wave is shorter than the microwave. For instance, the wavelength of the millimeter-wave in vacuum is only approximately 5 mm at 60 GHz. Conventionally, the side length for the typical patch antenna fabricated on a dielectric substrate is roughly 2 mm. Consequently, the level of fabrication precision and assembly alignment accuracy needed for the millimeter-wave antenna, in general, would be relatively higher than the microwave antenna. Since the array antenna module is constructed with a large number of units, the degree of difficulty in precision control would be even greater.
Taking into considerations the vigorous development of chip technology and the device volume, cost and the integration of antenna and chip, the antenna module can generally be manufactured by applying the technology of multi-layer low temperature co-fired ceramic (LTCC). The multi-layer LTCC technology can be used as the carrier board for the RF front-end chip, and the low-loss characteristic provides the circuit route for the millimeter-wave RF signal and the fabrication of a patch array antenna. However, the dielectric constant for the LTCC is relatively high, such as approximately 5 to 8, and the layers are thin. As a result, the gain for a single conventional patch antenna is just around 4-6 dBi. Therefore, in order to satisfy the system requirement, more units are required to form an array, and the number of units in array is usually between 16 and 64.
Although the single antenna module is able to reach a higher gain in array, nevertheless, the angular coverage for the main beam of the antenna is not sufficiently wide. Accordingly, applicability in the complex wireless communication environment will be extremely difficult.